1. Field of the Invention
The present invention relates to using image-guided surgery techniques to collect data to insure accurate tracking of an ablation device.
2. Background Information
For over fifty years, diagnostic images have been used for surgical guidance, especially in the field of neurosurgery. Image-guided surgery implements two fundamental ideas: first, the concept of an image-space to physical-space mapping or registration, and second, the use of an extracranial device for accurate surgical guidance without direct visualization. Such ideas gave birth to stereotactic neurosurgery, a technique for locating targets of surgical interest within the brain relative to an external frame of reference. This is traditionally defined as the temporary attachment of a mechanical frame to the skull or scalp in order to define a 3-D frame space around a patient. With the advent of computed tomography (CT), the coordinates of a target (i.e. tumor) in image space could be assigned coordinates in frame space if the CT images are obtained with the attached frame. Unfortunately, frames are uncomfortable to patients, must be applied prior to imaging, and are cumbersome in the imaging environment and the operating room.
These factors led to the development of frameless stereotactic surgical systems, or interactive, image-guided surgery (IIGS) systems. In traditional IIGS systems, present surgical position is tracked during an operation and displayed on pre-operatively obtained tomographic images. As the surgeon changes the current surgical position, displayed images are updated in real time. In one of the earliest IIGS systems, physical space surgical position was determined using articulated arms. The position of an articulated pointer was calculated using a personal computer (PC) and overlayed on tomographic images. Magnetic resonance images (MRI) and CT negative films are scanned into the computer and displayed as images on a video interface. Other early image-guided surgical systems also used electromechanical 3-D coordinate digitizers to indicate present surgical position on various representations of patient data, including 2-D transverse, coronal and sagittal CT or MRI slices, and on image renderings of the physical object surface. Since it was necessary to have computers capable of managing large volumes of image information (>100 Mbytes) and updating the display quickly, most early IIGS systems are were developed with VME bus devices running UNIX.
Early IIGS systems were developed on PCs using multiple processors. In a task-oriented asymmetric multiprocessing (TOAM) system developed in 32 bit extended DOS, discrete tasks such as physical space localization, data fetching, and display were conducted asynchronously on specialized processors which communicated with inexpensive, general purpose processors that worked as loaders and schedulers. For physical space localization, several articulated arms with six degrees of freedom were first developed. These cumbersome arm devices were eventually replaced with lightweight cylindrical pen-like probes which could be tracked more easily in the operating room using an optical triangulation system. The spatial location of the guidance instrument was determined using a collection of discrete processors which continually update the physical space location. This location was then passed to the central processor where it was mapped into image space. Once the image space map was complete, the appropriate tomographic slices were selected and displayed. Because this system was designed before the advent of large memory availability, image display relied heavily on hardware manipulation using disk controllers to load images directly from the hard drive. Control of the bus was passed from the main processor to the disk drive controller, where the correct image was fetched and sent to the display processor.
With the continuing increase in performance to price, processes which could only be performed on workstation class machines are now routinely performed on PCs. As the PC hardware evolved, however, it became apparent that DOS-based systems would not have the continuing support of hardware vendors.
Because of these considerations, a need for an operating room image-oriented navigation system (ORION) emerged. ORION was developed in Windows NT using MS Visual C++ 6.0 with the Win32 API. Not only was this system designed to be faster than the previous one, but it was not necessary to redesign the software with each hardware advance. Components of the system were developed as dynamic link libraries (DLLs), so that new technology could be incorporated into the system without a complete software rewrite. The system is also somewhat portable. It runs adequately on any PC with a 200 MHz or higher Pentium processor and 128 MB of memory which also has the appropriate video card and 3-D localizer hardware and software.
When designing an image-guided surgical system, it is critical that the precise location of an ablative instrument used to perform image-guided surgery be determined on a continuous basis (e.g., update rates approaching 30 frames per second). Further, in an effort to insure the utmost in precision, an ablation zone of the ablative instrument, the tissue being operated on, and a particular portion of the tissue to be resected or ablated during surgery must also be continuously and accurately tracked.
What is needed is a method and apparatus for collecting and processing physical space data for use while performing image-guided surgery, such that tumors and lesions in the tissue of a living patient can be accurately located, and resected or ablated with a precisely tracked ablative instrument. The present invention fulfills such a need.